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Exploited vulnerability · CISA KEV

Is CVE-2021-22991 exploited? Yes: in CISA KEV since 18 Jan 2022

Gociux · F5 BIG-IP Traffic Management Microkernel · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2021-22991, F5 BIG-IP Traffic Management Microkernel Buffer Overflow, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 18 Jan 2022, 293 days after it was published. It affects F5 BIG-IP Traffic Management Microkernel, an internet-facing product of the kind attackers use for initial access. If you run it, CISA's required action is: Apply updates per vendor instructions.

exploitedYesCISA KEV · 18 Jan 2022
ransomwareNot knownno confirmed use
EPSStop 1%among the most likely CVEs to be exploited
severity9.8CVSS 3.1 · critical
US federal due1 Feb 2022BOD 22-01 deadline

What it is

The Traffic Management Microkernel of BIG-IP ASM Risk Engine has a buffer overflow vulnerability, leading to a bypassing of URL-based access controls.

VendorF5 (8 exploited CVEs in KEV)
ProductBIG-IP Traffic Management Microkernel
VulnerabilityF5 BIG-IP Traffic Management Microkernel Buffer Overflow
WeaknessCWE-119
Published31 Mar 2021
Added to KEV18 Jan 2022
Reported by (CNA)f5

What to do

  1. Check whether you run it. Look for BIG-IP Traffic Management Microkernel in your asset inventory, including appliances and cloud images. Stack check lists every exploited F5 CVE at once.
  2. Apply the fix. Apply updates per vendor instructions.
  3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 31 Mar 2021.
  4. Get told next time. Email alerts when CISA adds a CVE for F5.

References

Questions

Is CVE-2021-22991 being exploited?

Yes. CISA added CVE-2021-22991 to the Known Exploited Vulnerabilities catalog on 18 Jan 2022, which means there is reliable evidence of exploitation in the wild.

Is CVE-2021-22991 used in ransomware attacks?

CISA does not list known ransomware use for it. That can change, and exploitation alone is reason to fix it first.

How do I fix CVE-2021-22991?

Apply updates per vendor instructions. Check F5's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected BIG-IP Traffic Management Microkernel and watch it for signs of compromise.

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in January 2022 · F5 scorecard · act-now radar.

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